Magic methods code

returnvalue · returnvalue · commit 74b07b1321cc · 2020-09-21T09:27:41.000-04:00
diff --git a/README.md b/README.md
@@ -37,4 +37,5 @@ files, and the full tutorial for each collection of code is available below. 
 30. [Abstract Base Classes](https://vegibit.com/python-abstract-base-classes/)
 31. [Multiple Inheritance In Python](https://vegibit.com/multiple-inheritance-in-python/)
 32. [Python Interface Design Pattern](https://vegibit.com/python-interface-design-pattern/)
-33. [Composition Over Inheritance](https://vegibit.com/composition-over-inheritance/)
+33. [Composition Over Inheritance](https://vegibit.com/composition-over-inheritance/)
+34. [What Are Python Magic Methods](https://vegibit.com/what-are-python-magic-methods/)
diff --git a/magicmethods.py b/magicmethods.py
@@ -0,0 +1,99 @@
+class Book():
+    def __init__(self, title, author, price):
+        super().__init__()
+        self.title = title
+        self.author = author
+        self.price = price
+
+    def __str__(self):
+        return f'{self.title} by {self.author}, costs {self.price}'
+
+    def __repr__(self):
+        return f'title={self.title},author={self.author},price={self.price}'
+
+    def __eq__(self, value):
+        if not isinstance(value, Book):
+            raise ValueError('Can\'t compare book to non-book type')
+
+        return (self.title == value.title and
+                self.author == value.author and
+                self.price == value.price)
+
+    def __ge__(self, value):
+        if not isinstance(value, Book):
+            raise ValueError('Can\'t compare book to non-book type')
+
+        return self.price >= value.price
+
+    def __lt__(self, value):
+        if not isinstance(value, Book):
+            raise ValueError('Can\'t compare book to non-book type')
+
+        return self.price < value.price
+
+    def __getattribute__(self, name):
+        if (name == 'price'):
+            price = super().__getattribute__('price')
+            discount = super().__getattribute__('_discount')
+            return price - (price * discount)
+        return super().__getattribute__(name)
+
+    def __setattr__(self, name, value):
+        if (name == 'price'):
+            if type(value) is not float:
+                raise ValueError('The "price" attribute must be a float')
+        return super().__setattr__(name, value)
+
+    def __getattr__(self, name):
+        return name + ' is not here!'
+
+    def __call__(self, title, author, price):
+        self.title = title
+        self.author = author
+        self.price = price
+
+
+book1 = Book('Python Crash Course', 'Eric Matthes', 23.99)
+book2 = Book('Serious Python', 'Julien Danjou', 25.43)
+book3 = Book('Automate the Boring Stuff with Python', 'Al Sweigart ', 26.99)
+book4 = Book('Python for Kids', 'Jason Briggs', 19.79)
+
+# print each object
+print(book1)
+print(book2)
+print(book3)
+print(book4)
+
+# use str() and repr()
+print(str(book1))
+print(repr(book2))
+
+# Check for equality
+print(book1 == book3)
+print(book1 == book2)
+print(book3 == book3)
+
+# Check for greater and lesser value
+print(book2 >= book1)
+print(book2 < book1)
+print(book3 >= book2)
+
+# Sorting books
+books = [book1, book3, book2, book4]
+books.sort()
+print([book.title for book in books])
+
+# Try setting and accessing the price
+book1.price = 37.95
+print(book1)
+
+book2.price = float(40)  # using an int will raise an exception
+print(book2)
+
+# If an attribute doesn't exist, __getattr__ will be called
+print(book1.randomprop)
+
+# call the object as if it were a function
+print(book1)
+book1('Learning Python', 'Mark Lutz', 44.94)
+print(book1)
